Ophthalmic microsurgical procedures frequently require precision cutting and/or removing of various body tissues of the eye. During the procedures, ophthalmic illumination probes may provide illumination for the surgical field. A user, such as a surgeon or other medical professional, may insert the probe into the eye to illuminate the inside of the eye. The probe delivers light using an optical fiber. Typically, the probe is connected to an optical port of an ophthalmic illumination system. The ophthalmic illumination system may be part of a surgical console and includes a light source. The illumination system may also include other optical elements, such as a condenser, that facilitate coupling the light into the probe's optical fiber.
During assembly of the ophthalmic illumination system, manufacturers try to optimize various parameters of the light beam. These parameters may include coupling efficiency, which describes how well the light is coupled into probe's optical fiber. High coupling efficiency corresponds to the desirable transmission of relatively greater amount of undistorted light from the light source to the surgical field, via the probe. Low coupling efficiency corresponds to less light being transmitted to the surgical field, as well as the light that is transmitted having an undesired angular profile. Other parameters that affect system performance include how well the light is transmitted within the fiber and the angular profile of the output beam that is transmitted to the surgical field.
One or more of these parameters may be influenced by the numerical aperture (“NA”) of the light beam. The NA is, generally speaking, a description of the width or diameter of a beam and may be referenced as a cone angle. The NA may also be used to describe the width or diameter of a beam that can be accepted by an optical fiber. For some light sources, such as a supercontinuum laser source, the NA of the beam is roughly proportional to wavelength. Thus, higher wavelength light has a higher NA and vice versa. Different light sources can also transmit light having different NAs. Differing beam diameters for different light sources and different wavelengths of light present challenges in manufacturing a system with consistent NA to consistently achieve high levels of coupling efficiency, high transmittance efficiency within the fiber, and desirable angular profiles for the output beam.
Various components of illumination systems, such as collimators, are typically designed to work best with light having a given beam diameter. For example, when a light beam has a collimated beam diameter that is larger than the intended beam diameter, the cone angle of light focused into the fiber will be larger as well. In general, the nominal collimated beam diameter may be maximized to completely angularly fill the acceptance NA of the fiber. Therefore, a collimated beam diameter that is larger than nominal will result in loss of efficiency within the fiber. Even if the beam is efficiently coupled into the fiber, at its first encounter with the core/cladding interface on the cylindrical side surface of the fiber, the high angle rays of the high NA beam above the fiber acceptance NA will be lost in the cladding. Similarly, if the collimated beam diameter is less than the nominal value, the beam will efficiently couple into and be efficiently transmitted through the fiber. However, its beam NA will be less than nominal, and therefore the beam emitted from the distal end of the fiber will have an angular spread that is less than desired. In both circumstances, there is a penalty for not having the collimated beam diameter be constant with wavelength at the nominal desired value. Achieving a consistent collimated beam diameter with different light sources across different wavelengths can be difficult.